Andon lights

[Pivotman]

I have been assigned the task of hooking up Andon lights on several machines and departments. I need to have two strobes one for maintenance and one for inspector. I am considering using a plc to track there state potentially so the system could be monitored at a central location. What is the longest I can run the sensors back to a central plc. Or would it make sense to have a plc in each department. Most of our machines are all relay logic and 120vac. Any sensors I would add I was planning on makeing 24vdc for safety and reliablity. Any other ideas would be appreaciated.

 

[Henneshoe]

Not exactly my field, but I believe most people choose a 4-20 mA output for sensors with long runs. Here is a thread discussing how far you can go with that. (Basically as far as you want as long as your wire gauge is thick enough and you have a high enough compliance voltage)

http://www.eng-tips.com/viewthread.cfm?qid=223908&page=1

Voltage mode sensors (0-10V for example) are going to be less immune to noise and the distance you can go depends on how noisy the environment is and the shielding on your cable.

You can also get sensors with a serial communication output. Specs for the distance these can travel will be in the datasheet.

Hope that helps.


Jim

 

[NWBeaver]

If you are just monitoring the state of a light, some discrete I/O would do the job, you really wouldn't need any sensors. I would think you just need to monitor the state of the circuit driving the light, such as a PLC output or a relay.

Are the lights you are planning to install, going to be hardwired to a selector switch, or do you plan to use PLC I/O?

In the case of hardwired lights, you could use a set of relay contacts wired back to a PLC input. This would also work in the case of a PLC output driving the light, you could bring a signal back to another PLC.

Discrete I/O can go fairly long distances, so you must just have all the lights controlled by one central PLC.

A series of small distributed PLC's all networked together is still another option.

Do you have existing PLC's and I/O available? I can think of a lot of ways to do this, do you want to try to use any existing hardware, or should this be kept separate?

 

[Pivotman]

NwBeaver

A few of the machines have Horner PLC's with availble io space. I have considered using several small plc's as well. My issue is most of the machines are controlled by relays. Almost all of my plc's are ethernet enabled which would make this very easy however that is the exception to most of my machines on the shop floor.

One of my biggest concerns is today I am just monitoring lights tomorrow I may be monitoring the individual machines for rate and parts counters. I just want to make sure I have a system that is expandable.

 

[NWBeaver]

Small modular PLC's with ethernet capabilties are fairly inexpensive now, and can provide plenty of room for expansion.
Depending on how many machines you have and their proximity to each other, a single PLC might easily handle all your needs.
It would be much cleaner to have all your monitoring on a single small PLC, and not have to mess with the existing programs and relays.

 

[NWBeaver]

I meant to say that could have all the lights controlled by one PLC, not must.

What type of central location monitoring are you considering?

 

[kphilman]

You know one option for something like this is to buy something like an AB compactlogix and then use point IO RIO over ethernet, the point IO is fairly well priced and is reliable and then you have about unlimited possibilties and have something fairly universal and simple to use